Identification of X‐Ray Point Sources and a Study of the Nature of 62 X‐Ray Globular Cluster Candidates in M31

This paper includes two parts. The first is to present the spectral energydistributions (SEDs) of 49 globular cluster (GC) X-ray sources in the BATC 13intermediate-band filters from 3800 to 10000 A, and identify 8 unidentifiedX-ray sources in M31. Using the X-ray data of Einstein observation from 1979 to1980, ROSAT HRI observation in 1990, Chandra HRC and ACIS-I observations from1999 to 2001, and the BATC optical survey from 1995 to 1999, we find 49 GCX-ray sources and 8 new unidentified X-ray sources in the BATC M31 field. Byanalyzing SEDs and FWHMs, 4 of the 8 X-ray sources may be GC candidates. Thesecond is to present some statistical relationships about 62 GC X-ray sources,of which 58 are already known, and 4 are identified in this paper. Thedistribution of M31 GC X-ray sources' V mags is bimodal, with peaks at m_v =15.65 and m_v = 17.89, which is different from the distribution of GCcandidates. The distribution of B-V color shows that,the GC X-ray sources seemto be associated preferentially with the redder GCs, in agreement with theprevious results. Kolmogorov-Smirnov test shows that the maximum value of theabsolute difference of B-V distributions of GC X-ray sources and GCs isD_{max}=0.181, and the probability P=0.068 which means we can reject thehypothesis that the two distributions are the same at the 90.0% confidencelevel. In the end, we study the correlation between X-ray luminosity (0.3-10keV) and the optical luminosity (in V band) of the GC X-ray sources in M31, andfind that there exits a weak relationship with the linear correlationcoefficient r = 0.36 at the confidence level of 98.0%.Comment: Accepted for publication in the November 2005 issue of the PASP. 19 pages, 8 figures including 2 jpg figure